The present invention relates to work vehicle hitches. In particular, the present invention relates to upper and lower links of a work vehicle hitch and methods for manufacturing such links.
Three-point hitches are employed at the rear or the front of work vehicles to lift, carry, pull and push implements or equipment attached to the work vehicle. Three-point hitches generally include linkages for attaching the equipment or implement to the work vehicle. Such linkages include an upper link and two lower links. Each link has an arm with a first end articulately connected to the work vehicle at a link point and a second end articulately connected to the implement at a hitch point.
To provide for articulation at the link point and the hitch point, the first and second ends each include a ball and socket joint formed by a bushing ball captured within a socket of the arm. The ball includes an opening therethrough which receives an attachment pin connected to the work vehicle at the link point or the implement at the hitch point.
FIGS. 1 and 2 illustrate a conventional lower or draft link 10 formed by conventional processes. As shown by FIGS. 1 and 2, link 10 includes a three-piece arm 12 and bushing balls 14, 16. Arm 12 includes member 18 and insert rings 20, 22. Member 18 is formed from wrought or forged medium carbon alloy steel which is machined to form semi-spherical surfaces 34. Insert rings 20, 22 are formed from wrought or forged low carbon alloy steel which is machined to form semi-spherical surfaces 36. After being machined, rings 20, 22 are case hardened to approximately 57-65 Rockwell C. Member 18 is hardened to a lesser hardness of approximately 40 Rockwell C so as have adequate toughness to resist high tensile loads. Member 18 and insert rings 20, 22 are then joined to form sockets 24, 26 at ends 28, 30 of link 10. In particular, link 10 is formed by pressing surfaces 34, 36 together with one of balls 14, 16 captured therebetween. The ends of the member 18 are then deformed or swedged at 38 to permanently affix the insert rings 20, 22 to member 18.
Conventional wisdom teaches that the wear of bushing balls 14, 16 and arm 12 is caused by abrasive particles, such as dust, trapped between bushing balls 14, 16 and sockets 24, 26. As a result, both bushing balls 14, 16 and socket inserts 20, 22 are designed to be as hard as the abrasive particles to resist such abrasive wear. Consequently bushing balls 14, 16 are hardended to a hardness of approximately 57-65 Rockwell C and spherical surface 36 of insert rings 20, 22 is also hardened to approximately 57-65 Rockwell C.
Although such links and the above process used to manufacture such links have been employed for many years, such links are difficult and costly to manufacture, are structurally weak at the link and hitch points, and are costly to repair and replace. As described in detail above, forming each ball and socket joint requires multiple processes such as forging, machining, heat treating and swedging. Each process and step adds to the manufacturing cost. In addition, because each ball is merely retained in place by the swedges securing the insert ring to the end of the arm, and because the cross section of member 18 at ends 28, 30 is reduced to accommodate insert rings 20, 22 the socket joints at the link and hitch points are inherently structurally weak. Moreover, because the hardness of the ball and the insert ring are substantially the same, the contacting surfaces of the ball and the ring will wear at the same rate. Once either the ball or the socket formed by the ring at either the first end or the second end of the link sufficiently wear, the entire link must be replaced. Replacement of the entire link is inconvenient and costly.
Thus, there is a continuing need for upper and lower links which are easy and inexpensive to manufacture, which are strong at the link and hitch points and which are inexpensive to repair and refurbish when worn.
The present invention provides a link for a hitch of a work vehicle. The link includes at least one elongate arm having a first end adapted for being coupled to the work vehicle and a second end adapted for being coupled to an implement either directly, or indirectly via a quick coupler. At least one of the first and second ends includes a socket integrally formed as part of a single unitary body. The link further includes a ball removably retained within the socket. The socket includes at least one passage through which the ball is insertable into the socket and removable from the socket.
The present invention also provides a link for a hitch of a work vehicle. The link includes an elongate arm having a first end adapted for being coupled to the work vehicle and a second end adapted for being coupled to an implement. At least one of the first and second ends includes a socket and a ball received within the socket. The socket has a first surface formed from a metal having an auspherite matrix and graphite. The ball has a second surface facing the first surface. As a result, the metal of the first surface resists adhesive wear of the socket from contact with the ball.
The present invention also provides an arm for use with the ball having a first surface to form a link of a work vehicle hitch. The arm includes an elongate member having a first end adapted for being coupled to the work vehicle and a second end adapted for being coupled to an implement. At least one of the first and second ends includes a socket. The socket has a second surface adapted to face the first surface of the ball when the ball is received within the socket. The second surface is formed from a metal having an ausferrite matrix and dispersed graphite spheroids. The metal resists adhesive wear of the socket from contact with the ball.
The present invention also provides a method for forming a link for a hitch of a work vehicle. The method includes the steps of providing at least one mold member having a cavity defining an elongate arm having first and second ends and at least a portion of a socket surface at the first end configured to receive a ball, depositing a molten material into the cavity, solidifying the molten material in the cavity and removing the at least one mold member from about the solidified material.